Microfluidic systems such as microfluidic devices, cartridges, packages, lab-on-a-chip (LOC) and micro total analysis system (micro-TAS) for example require fluidic dispensing control to realize particular protocol. Fluidic dispensing control includes controlling of the fluids' flow sequence, flow duration, flow direction and flow rate. A microfluidic system with multiple fluids or reagents needs to have a mechanism to control dispensing of each fluid or reagent so as to follow individual flow protocol. At the same time, the reagents' cross mixing arising to contamination in the microfluidic system should be avoided.
Some other microfluidic systems require pre-storage of reagents in integrated reservoirs. Besides storage function, these reservoirs also need dispensing mechanism, which pushes the reagents into the microfluidic system during operation. After the reagents are fully dispensed, the dispenser should close to avoid flow of other reagents into the reservoir.
Several attempts have been made to control the flow of each fluid or reagent in a microfluidic system with multiple fluids or reagents. Amongst them are different types of valves which can control the dispensing of respective fluids or reagents in a microfluidic system. One approach is described in the publication “Miniaturization of pinch type valves and pumps for practical micro total analysis system integration”, Kwang W. O. et al, J. MicroMech and MicroEng. 15 (2005), pp 2449-2455. This publication discloses a miniaturized pinch-type valve which is surface mountable on microfluidic LOC devices. The pinch-type valve consists of a solenoid magnetic actuator with a pinch plunger and a biomedical grade silicone tube. According to this publication, magnetic force is used to manipulate the pinch plunger to open and close the silicone tube or channel, thereby controlling the flow of fluid.
The publication “Disposable Smart Lab on a Chip for Point-of-Care Clinical Diagnostics”, Chong H. A. et al, Proceedings of the IEEE, Vol. 92, No. 1, (January 2004), pp. 154-173 discloses a micro-dispenser module in a microfluidic LOC device. A sample fluid volume is loaded into the fixed-volume metering micro-dispenser, which in turn dispenses an exact volume of liquid for further biochemical analysis. The sample fluid is introduced through a fluid inlet at a low flow rate. The fluid passes through a first passive valve and a narrow channel to enter a reservoir. A second passive valve at the end of the reservoir prevents the fluid from leaving the reservoir. As long as the applied fluid driving pressure is less than the pressure required to overcome the second passive valve, the fluid will be contained completely within the reservoir. According to this publication, applied fluid driving pressure and passive valve are used to control fluid flow within the reservoir.
The publication “Disposable Bio-microfluidic package with passive fluidic control”, Ling Xie et al, Electronics Packaging Technology Conference, 7-9 Dec. 2005, discloses a disposable bio-microfluidic package using passive valves for fluidic control. The passive valve is embedded in micro-channel structures and controls the fluid flow without any actuators. The key principle of the passive valve is that the fluid flow through a main channel and surface tension causes the fluid to stop before a valve gap. The valve is closed in the initial stage. To open the valve, a threshold pressure is applied. Fluid will then pass through the valve. According to this publication, threshold pressure and passive valve are used to control fluid flow within a disposable bio-microfluidic package.
The publication “Development of an integrated Bio-microfluidic package with micro-valves and reservoirs for a DNA Lab on a Chip (LOC) Application”, Ling Xie et al, Electronic Components and Technology Conference, 30 May-2 Jun. , 2006, discloses a bio-microfluidic package with integrated reservoir and valves for LOC application. A passive valve is embedded in a channel and the valve is activated by pressure. At storing condition, the valve is closed to prevent reagent flowing from a reservoir to the channel. Once fluidic pressure in the reservoir increases and reaches the threshold pressure, the valve opens. The valve is passive and therefore controls the fluid flow without any moving parts. According to this publication, threshold pressure and passive valve are also used to control fluid flow within a disposable bio-microfluidic package.
U.S. patent application Ser. No. 11/096,035 discloses microfluidic circuits including triggerable passive valves, connected in series or in parallel. A triggerable passive valve arrangement includes a flow restrictor, a pressurizing device, and a passive valve, connected with a fluid delivery channel. The triggerable passive valve acts upon a sample liquid. As the sample liquid flows into the fluid delivery channel, it stops at the passive valve. For flow to occur beyond the passive valve, the pressure of the sample liquid must exceed the burst pressure of the passive valve. The burst pressure of the passive valve is determined by its geometry and physical properties. The pressurizing device exerts pressure on the sample liquid when activated, increasing its pressure to a value higher than the burst pressure of the passive valve, causing the sample liquid to move past the passive valve. Most of the sample liquid flows in the direction of the passive valve, rather than in the direction of the flow restrictor. This is because the flow restrictor has a higher resistance to flow once the passive valve has been breached. Once flow beyond the passive valve occurs, the pressure exerted upon the sample liquid by the pressurizing device can be removed. According to U.S. patent application Ser. No. 11/096,035, applied fluid driving pressure and passive valve are used to control fluid flow.
U.S. patent application Ser. No. 09/985943 discloses microfluidic flow control devices. Each microfluidic flow control device includes a regulating device having two overlapping channel segments separated by a deformable membrane in fluid communication with one another. The deformable membrane is responsive to changes in pressure between two channel segments. When the pressures in the channel segments are substantially the same, the deformable membrane adopts a neutral position. If the pressure in either channel segment is increased, then the deformable membrane will deform towards the other channel segment. According to U.S. patent application Ser. No. 09/985,943, the regulating device uses pressure to control the direction of deformation of the membrane, thereby controlling the flow of fluid.
Controlling the dispensing of fluid and fluid flow rate in prior art devices to prevent back flow and cross mixing of fluids is difficult. It is also tough to maintain a low dead volume in the prior art devices. These difficulties in controlling the dispensing of fluid may lead to contamination of different fluids in microfluidic systems. Therefore, an objective of the present invention is to provide an alternative dispenser arrangement that can control dispensing of fluid and fluid flow rate in microfluidic systems, thereby advantageously avoids or reduces some of the above-mentioned drawbacks of prior art devices.